Police have arrested a fifth suspect near Manchester following the bombing at an Ariana Grande concert that left at least 22 people, including children, dead and 119 injured.

Sixty-four people still remain hospitalized.

Manchester police made three other arrests Wednesday morning.

The arrests come as armed soldiers are being deployed to key sites around the United Kingdom as the country moves to its highest alert level for the first time in a decade.

British Prime Minister Theresa May raised the terror threat level to "critical" and warned a "further attack may be imminent," but also said her people will not live in fear.

"All acts of terrorism are cowardly attacks on innocent people,” says May. “But this attack stands out for its appalling, sickening cowardice. Let us remember those who died and let us celebrate those who helped, safe in the knowledge that the terrorists will never win.”

Police have identified the suspected bomber as 22-year-old Salman Abedi. According to police, Abedi set off an improvised explosive device outside Manchester Arena at the end of the concert. Prime Minister May says he is believed to have acted alone but a wider group of individuals could be linked to the attack. Police believe Abedi died in the blast, but say he hasn't formally been identified by the coroner.

According to sources, Abedi was of Libyan descent, but born and raised in the UK and was a student at the University of Salford in Manchester. ISIS has claimed responsibility for the attack, but at this point, authorities have found no evidence linking Abedi with the terror group.

As for security, soldiers were seen in the grounds of Buckingham Palace early Wednesday morning, as officials have announced military personnel will guard "key locations" as part of what's been called "Operation Temperer."